Pairwise measurements for improved position determination

ABSTRACT

Approaches for enhancing range-based position determination using pairwise error detection and compensation are provided. One method for enhancing a position estimate of a first node may include performing measurements at the first node using a signal received from a second node, and receiving measurements from the second node. The received measurements may be performed at the second node using a signal provided by the first node. The method may further include determining pairwise comparisons of the performed measurements and the received measurements, and compensating the measurements performed at the first node, based on the pairwise comparisons, for estimating the position of the first node. Systems and apparatuses for performing the various position determination methods are further presented.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present application for patent is a divisional of patent applicationSer. No. 13/725,078, entitled “Pairwise Measurements for ImprovedPosition Determination”, filed Dec. 21, 2012, pending, and assigned tothe assignee hereof and hereby expressly incorporated by referenceherein.

FIELD OF DISCLOSURE

Aspects of this disclosure generally relate to position determinationtechniques in wireless communication systems. Specifically, thedisclosure provides approaches for improving range-based positiondetermination using pairwise error detection and compensation.

BACKGROUND

Mobile stations offer sophisticated capabilities for determining theirposition using a variety of resources, including those resourcesprovided by wireless communication networks. New software applicationsresiding on mobile stations, such as those related to personalproductivity, social networking, advertising, e-commerce, and/or otherforms of data acquisition, may utilize position information to providenew features and services to consumers. Moreover, some regulatoryrequirements of various jurisdictions may require a network operator toreport the location of a mobile station for emergency services.

In conventional digital cellular networks, position location capabilitycan be provided by various time and/or phase measurement techniques. Forexample, in CDMA networks, one position determination approach used isAdvanced Forward Link Trilateration (AFLT). Using AFLT, a mobile stationmay compute its position from phase measurements of pilot signalstransmitted from a plurality of base stations. Improvements to AFLT havebeen realized by utilizing hybrid position location techniques, wherethe mobile station may employ a Satellite Positioning System (SPS)receiver. The SPS receiver may provide position information independentof the information derived from the signals transmitted by the basestations. Moreover, position accuracy can be improved by combiningmeasurements derived from both SPS and AFLT systems using conventionaltechniques.

However, conventional position location techniques based upon signalsprovided by SPS and/or cellular base stations may encounter difficultieswhen the mobile station is operating within a building and/or withinurban environments. In such situations, signal reflection andrefraction, multipath, and/or signal attenuation can significantlyreduce position accuracy, and can slow the “time-to-fix” to unacceptablylong time periods. These shortcomings may be overcome by having themobile station exploit signals from other types of wireless networks,such as Wi-Fi (e.g., IEEE 802.11x standards) or WiMAX (e.g., IEEE 802.16standards), to derive position information. Conventional positiondetermination techniques used in these other types of wireless networksmay utilize range-based position determination techniques. Therange-based position determination techniques may estimate distanceinformation using Round Trip Time (RTT) measurements and/or signalstrength measurements (e.g., Received Signal Strength Indicator (RSSI))derived from signals utilized within such networks. The range basedposition determination may be used for any network device within thesenetworks, such mobile stations and/or access points (APs) which areplaced at unknown positions. However, indoor environments can presentchallenges for reliable range measurements due to the complexity of theradio frequency (RF) environment and multipath.

Moreover, the network devices themselves may introduce various biasesthat can affect range determination. For example, RTT measurementtechniques may be affected by time biases introduced by time delaysincurred as wireless signals propagate through various devices in thenetwork. Utilizing RSSI measurements for accurate ranging may beaffected by amplitude biases introduced by transmission powerdifferences and/or various gains used in RF and signal processing pathsof network devices. In practice, when employing conventional range-basedpositioning techniques, estimating and removing time and amplitudebiases may involve time-consuming pre-deployment fingerprinting and/orcalibration of the network devices.

Accordingly, it may be desirable to implement efficient compensationtechniques which can address time and amplitude biases to improverange-based position determination, while avoiding costly pre-deploymentefforts and/or changes to the network infrastructure.

SUMMARY

Aspects of the invention are directed to systems and method forimproving range-based position determination using pairwise errordetection and compensation.

In one aspect, a method for enhancing a position estimate of a firstnode is presented. The method may include performing measurements at thefirst node using a signal received from a second node, and thenreceiving measurements from the second node, where the receivedmeasurements are performed at the second node using a signal provided bythe first node. The method may further include determining pairwisecomparisons of the performed measurements and the received measurements,and then compensating the measurements performed at the first node,based on the pairwise comparisons, for estimating the position of thefirst node.

In another aspect, a first node which determines an enhanced positionestimate using pairwise measurements is presented. The first node mayinclude a wireless transceiver, a processor coupled to the wirelesstransceiver, and a memory coupled to the processor. The memory may storeexecutable instructions and data for causing the processor to performmeasurements at the first node using a signal received from a secondnode, and then receive measurements from the second node, wherein thereceived measurements are performed at the second node using a signalprovided by the first node. The instructions may further configure theprocessor to determine pairwise comparisons of the performedmeasurements and the received measurements, and compensate themeasurements performed at the first node, based on the pairwisecomparisons, for estimating the position of the first node.

In a further aspect, another method for enhancing a position estimate ofa first node is presented. The method may include receiving Round TripTime (RTT) and Received Signal Strength Indicator (RSSI) measurementsfrom a plurality of neighboring nodes, wherein the RTT and RSSImeasurements are performed at the neighboring nodes using a signalprovided by the first node. The method may further include evaluatingthe quality of the RTT and RSSI measurements received from theneighboring nodes, and performing pairwise comparison and compensationwith each neighboring node associated with the RTT and/or RSSImeasurements which fail the evaluating. The method may further includedetermining a position estimate of the first node based on the RTTmeasurements and RSSI measurements which pass the evaluating. The methodmay further include comparing information based on the RTT measurementsand/or the RSSI measurements with information derived from thedetermined position estimate, and performing pairwise comparison andcompensation with each neighboring node associated with RTT measurementsand/or RSSI measurements which compare unfavorably.

In another aspect, a first node which triggers an enhanced positionestimate using pairwise measurements is presented. The first node mayinclude a wireless transceiver, a processor coupled to the wirelesstransceiver, and a memory coupled to the processor. The memory storesexecutable instructions and data for causing the processor to receiveRound Trip Time (RTT) and Received Signal Strength Indicator (RSSI)measurements from a plurality of neighboring nodes. The RTT and RSSImeasurements may be performed at the neighboring nodes using a signalprovided by the first node. The instructions may further cause theprocessor to evaluate the quality of the RTT and RSSI measurementsreceived from the neighboring nodes, and perform pairwise comparison andcompensation with each neighboring node associated with the RTT and/orRSSI measurements which fail the evaluating. The instructions mayfurther cause the processor to determine a position estimate of thefirst node based on the RTT measurements and RSSI measurements whichpass the evaluating. The instructions may further cause the processor tocompare information based on the RTT measurements and/or the RSSImeasurements with information derived from the determined positionestimate, and perform pairwise comparison and compensation with eachneighboring node associated with RTT measurements and/or RSSImeasurements which compare unfavorably.

In yet another aspect, a method for enhancing a position determinationperformed by a server is presented. The method may include receivingmeasurements from a node based on signals received from a plurality ofneighboring nodes, and receiving signal measurements from a plurality ofneighboring nodes based on signals received from the node. The methodmay further include determining a pairwise comparison of themeasurements from the node and the measurements from each neighboringnode. The method may further include compensating the measurementsreceived from the node based on the pairwise comparisons, anddetermining the position estimate of the node using the compensatedmeasurements.

In another aspect, a server which enhances a position determination of anode using pairwise measurements is presented. The server may include anetwork interface, a processor coupled to the network interface, and amemory coupled to the processor. The memory may store executableinstructions and data for causing the processor to receive measurementsfrom a node based on signals received from a plurality of neighboringnodes, and receive signal measurements from a plurality of neighboringnodes based on signals received from the node. The instructions mayfurther cause the processor to determine a pairwise comparison of themeasurements from the node and the measurements from each neighboringnode, compensate the measurements received from the node based on thepairwise comparisons, and determine the position estimate of the nodeusing the compensated measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description ofembodiments of the invention and are provided solely for illustration ofthe embodiments and not limitation thereof.

FIG. 1 is a diagram introducing the concepts of pairwise comparison andcompensation (PCC) within an exemplary indoor wireless networkingenvironment.

FIG. 2 depicts diagrams illustrating exemplary configurations of varioustypes of nodes in a wireless network.

FIG. 3 is a diagram of an exemplary large scale operating environmentfor a mobile station which may communicate with local area wirelessnetworks and wide area wireless networks.

FIG. 4 is a block diagram illustrating various components of anexemplary mobile station.

FIG. 5 is a block diagram illustrating various components of anexemplary access point.

FIG. 6 is a block diagram illustrating various components of anexemplary positioning server.

FIG. 7 is a flowchart showing an exemplary process for pairwisecomparison and compensation of ranging measurements.

FIG. 8 is a flowchart showing an exemplary process for pairwisecalibration when a neighboring node is pre-calibrated.

FIG. 9 is a flowchart showing an exemplary process triggering pairwisecomparison and compensation.

DETAILED DESCRIPTION

Aspects of the invention are disclosed in the following description andrelated drawings directed to specific embodiments of the invention.Alternate embodiments may be devised without departing from the scope ofthe invention. Additionally, well-known elements of the invention willnot be described in detail or will be omitted so as not to obscure therelevant details of the invention.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Likewise, the term “embodiments ofthe invention” does not require that all embodiments of the inventioninclude the discussed feature, advantage or mode of operation.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of embodiments ofthe invention. As used herein, the singular forms “a”, “an” and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise. It will be further understood that theterms “comprises”, “comprising,”, “includes” and/or “including”, whenused herein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Further, many embodiments are described in terms of sequences of actionsto be performed by, for example, elements of a computing device. It willbe recognized that various actions described herein can be performed byspecific circuits (e.g., application specific integrated circuits(ASICs)), by program instructions being executed by one or moreprocessors, or by a combination of both. Additionally, these sequence ofactions described herein can be considered to be embodied entirelywithin any form of computer readable storage medium having storedtherein a corresponding set of computer instructions that upon executionwould cause an associated processor to perform the functionalitydescribed herein. Thus, the various aspects of the invention may beembodied in a number of different forms, all of which have beencontemplated to be within the scope of the claimed subject matter. Inaddition, for each of the embodiments described herein, thecorresponding form of any such embodiments may be described herein as,for example, “logic configured to” perform the described action.

FIG. 1 is a diagram introducing the concepts of Pairwise Comparison andCompensation (PCC) used in a wireless network that is placed in anindoor environment 100. The environment may include any number ofwireless devices 101-105 which may transmit and receive wireless signalsfor exchanging information in a wireless local area network. Thewireless devices 101-105 are referred to herein as “nodes,” (e.g., n(1)though n(5) as shown in FIG. 1), and each node may be, for example, anaccess point (AP) or a mobile station (MS). The nodes n(1) 101 throughn(5) 105 can communicate with each other over wireless channels 112-115using any known wireless protocol (e.g., 802.11) or combinationsthereof.

In addition to exchanging information over the wireless channels112-115, one or more nodes n(1) 101 through n(5) 105 may estimate theirposition using measurements derived from signals received fromneighboring nodes. Such measurements may use known techniques forexploiting the physical properties of the received signals to estimatedistances (defined herein as “ranges”) between a node and itsneighboring nodes. Once these ranges are known, further processing(which may also utilize pre-established information regarding the layoutof the network) can estimate a position of a node using knownrange-based position determination techniques. The ranges may beestimated by exploiting different physical characteristics of thereceived signal, and can include utilizing amplitude, propagation time,and/or phase information of the signals exchanged between nodes. Forexample, ranges may be derived from Round Trip Time (RTT) measurements.Ranges may also be derived from Received Signal Strength Indicator(RSSI) measurements of the signals received at a node for which alocation is desired. Embodiments may also utilize combinations of RSSIand RTT approaches. Alternative aspects may utilize any other knownranging techniques or combinations thereof. Examples of known time-basedranging techniques may include Time of Arrival (TOA), Time Difference ofArrival (TDOA), Observed Time Difference of Arrival (OTDOA), and/orAdvanced Forward Link Trilateration (AFLT). Examples of knownpower/amplitude ranging techniques may utilize Signal-to-Noise Ratio(SNR), Carrier-to-Noise Ratio (CNR), and/or Signal-to-Interference andNoise Ratio (SINR).

For example, as shown in FIG. 1, node n(1) 101 may determine rangesr(2:5) by communicating wirelessly with neighboring nodes n(2:5) 102-105using RF signals (e.g., 2.4 GHz), and standardized protocols for themodulation of the RF signals and the exchanging of information packets(e.g., IEEE 802.11). (Note: as used herein below, array notation x(m:n)is an abbreviated way of representing the set of values {x(m), x(m+1),x(m+2), . . . , x(n−2), x(n−1), x(n)}, where m<n.) Once the rangesr(2:5) are determined using RSSI and/or RTT measurements, node n(1) 101can then solve for its position by using a variety of known positioningtechniques, such as, for example, trilateration, sequential leastsquares, multi-dimensional scaling, and/or particle filtering (PF). Froma geometric perspective, it can be seen that the position node n(1) 101ideally lies at the intersection of circles having radii defined by theranges r(2:5) with centers at the locations of neighboring nodes(2:5)102-105. In practice, the intersection of these circles may not lie at asingle point due to the noise and other uncertainties/errors in thenetworking system.

Further referring to FIG. 1, the indoor environment 100 may presentchallenges for deriving the ranges r(2:5) because obscurations can causesignal interference that creates multipath and/or attenuates thereceived signals, which can adversely affect both RTT and RSSImeasurements. As can be seen in FIG. 1, node n(2) 102 and node n(5) 105are enclosed in different rooms, thus signals exchanged between thesenodes and node n(1) 101 will experience some attenuation when passingthrough one or more walls. Node n(3) 103 has clear line of sight to noden(1) 101, and thus range measurements derived from signals exchangedover wireless channel 113 will likely be more accurate and consistentthan those measurements derived from signals exchanged over wirelesschannel 112 and wireless channel 115. In each of the above noted cases,signal exchanges over wireless channels 112, 113, and 115 will be moreor less symmetric. That is, the signals transmitted from node n(1) 101and received by node (2) 102, node (3) 103, node (5) 105 will undergosimilar effects as signals transmitted in the reverse direction, sincethe wireless channels 112, 113 and 115 are effectively symmetric.However, signals exchanged between node n(1) 101 and node n(4) 104 maynot undergo the same degradations in both directions, as wirelesschannel 114 is not “as symmetric” as wireless channels 112, 113, and115, due to the relative location of an object 120 and wall 122, as willbe explained as follows.

Signals received at node n(4) 104 over wireless channel 114, which aretransmitted by node n(1) 101, may only experience attenuation by object120. Signals reflected off (not shown) object 120 transmitted by noden(1) 101, will not be received by node (4) 104. However, signalstransmitted by node n(4) 104 and received by node n(1) 101 mayexperience multipath due to reflections between object 120 and wall 122,in addition to being attenuated by object 120. Because signalsexperience different types of interference depending upon the directionof travel in wireless channel 114, measurements to derive range may beadversely affected between the node pair of node n(1) 101 and node n(4)104, and thus position determination accuracy can be reduced. Wirelesschannels having characteristics which vary based on the direction ofsignal propagation are referred to herein as “asymmetric wirelesschannels.” Techniques for addressing the adverse effects of asymmetricwireless channels on position determination are provided herein and arereferred to as “Pairwise Comparison and Compensation (PCC).”

A top level description of PCC immediately follows, with more detailedexplanations being presented below in the following description andsubsequent FIGS. 2-10. PCC can address adverse effects of asymmetricwireless channels, and can address ranging errors introduced by temporalchannel variation, and/or device measurement errors such as theTurnaround Clock Factor (TCF) error in RTT measurements. As used herein,the TCF may be defined as the residual of the RTT measurement minus thesum of forward and reverse time of flight. In other words, the TCF isany additional time delay caused by the responding device, which is theamount of time between the responding device's reception of signal andits subsequent transmission of the response signal back to theoriginating device.

PCC may initially start out by taking one or more pairwise measurementsbetween a node of interest (hereinafter the “node”) and one or moreneighboring nodes. The pairwise measurements may include RSSI and/orRTT, and typically include data from both sides of the wireless channel,to be collected at the node for subsequent comparison and compensation.Once the pairwise measurements are collected, they may be compared todetect and reject outlier measurements, and/or to generate correctionfactors. The correction factors may be applied to the measurements priorto determining range, thus producing better range estimates andsubsequently improved position estimates. In one example, the comparisonoperation may simply take the form of subtracting the pairwisemeasurements to generate a bias value, where the bias value is thenapplied to correct the measurement for range determination.

For example, further referring to FIG. 1, the PCC process may start bymaking pairwise measurements between node n(1) 101 and neighboring noden(2) 102. This may be accomplished by having node n(1) 101 transmit asignal to node n(2) 102 requesting a measurement m(2,1) to be made atnode n(2) 102. The requested measurement m(2,1) at node n(2) 102 is madebased on the signal transmitted by node n(1) 101. Once the measurementm(2,1) is complete, it may be sent back to node n(1) 101 over thewireless channel 112. Node n(1) 101 may then generate measurement m(1,2)based on the signal transmitted by node n(2) 102 over wireless channel112. The resulting pair of measurements {m(1,2), m(2,1)} is a singlepairwise measurement over wireless channel 112. This process may berepeated a number of times over the same wireless channel 112 (e.g.,5-10 times) to create adequate sample statistics. The same pairwisecollection process may be repeated between node n(1) 101 and the otherneighboring nodes n(3:5) 103-105 to collect pairwise measurements forthe other wireless channels 113-115. Once a sufficient number ofpairwise measurements have been collected for each wireless channel, themeasurements may be compared to remove outliers, and subsequentlyprocessed to generate bias values for compensating (i.e., adjusting) themeasurements m(1,2:5) made by node n(1) 101 to improve the rangeestimates for ranges r(2:5). Upon determining compensated rangeestimates for ranges r(2:5), a more accurate position estimate of noden(1) 101 may be determined.

As noted above, the pairwise measurements may be RSSI and/or RTTmeasurements taken at opposite ends of a wireless channel for a givennode pair. The pairwise comparison can be effective for detectingpersistent range measurement errors originated from device itself. Incase of RTT, certain APs may have outstanding TCF (turnaround clockfactors) compared to its peers, which cannot be detected by itself, butmay be detectable through pairwise comparison.

Accordingly, the two-sided data collection, comparison, and compensationapproach described above can provide: 1) error detection and outlierexclusion of measurements used to determine range; 2)compensation/adjustment of measurements to improve accuracy of rangeestimation, and subsequently improved position determination; and 3)permit calibration values of nodes which have been pre-calibrated (suchas APs) to be “propagated” to other uncalibrated nodes so that theircalibration of these nodes may be performed “on the fly.”

The above description merely provides an example scenario forillustrating the concepts of PCC techniques for enhancing range-basedposition determination. It should be understood that PCC techniquescould be used with any number of network nodes using any known wirelessnetworking protocols, including local area networking (IEEE 801.11)and/or wide area networking protocols (e.g., 3GPP2, LTE, WiMAX, etc.).Moreover, the PCC techniques are not necessarily limited to indoorenvironments, and thus may also be used in outdoor environments.

FIG. 2 depicts diagrams illustrating exemplary configurations of nodesin a wireless network. As noted above, each node within a network maybenefit from Pairwise Comparison and Compensation (PCC) to improveposition determination. Each node in the network may be any type ofwireless device, which could include one or more mobile stations (MSs)and/or one or more access points (APs) in any type of configuration. Forexample, configuration 200A depicts an MS 201A acting as a node ofinterest, with neighboring nodes being APs 202A, 203A, and 204A. In thisconfiguration, MS 201A may form pairs with APs 202A, 203A, and 204A forperforming PCC. Alternatively, any node in configuration 200A mayinitiate and collect pairwise measurements in configuration 200A.

Configuration 200B shows APs 201B-204B acting as nodes in the network.Since the APs may wirelessly communicate with each other, any AP mayinitiate the PCC process with its neighboring APs to better establishits position. This type of network configuration may also be called apeer-to-peer configuration. In other embodiments, the PCC process may beused to propagate calibration information from APs which have beencalibrated, to other APs which have not been calibrated, or to APs whichmay wish to have their calibration information updated. Propagating thecalibration information is discussed in more detail below in thedescription of FIG. 8.

Further referring to FIG. 2, in another exemplary configuration 200C,each node within the network may be an mobile station (MS). The MSs201C-204C may communicate with each other over their respective wirelesschannels in a “peer-to-peer” scenario, and any pair can initiate PCC toimprove its position determination accuracy.

In each of the above embodiments, the PCC process can be performed on anode of interest (also referred to herein as “the node”) whichcommunicates with its neighboring nodes to generate and collect theappropriate pairwise measurements. However, in other embodiments, PCCoperations may be performed by a server (hereinafter referred to as a“positioning server”) which can receive the pairwise measurements andperform the comparisons, and generate compensation values (e.g., biases)for use in compensation. The positioning server may then update thevarious nodes in the network with the appropriate values so theirmeasurements may be compensated to improve range calculations and thussubsequent position determination.

FIG. 3 is a diagram of an exemplary large scale operating environment300 for a mobile station 301 which may perform Pairwise Comparison andCalibration (PCC) with local area wireless networks and/or wide areawireless networks. The operating environment 300 may contain one or moredifferent types of wireless communication systems and/or wirelesspositioning systems as described in detail below. The mobile station 301may include one or more dedicated Satellite Positioning System (SPS)receivers specifically designed to receive signals for derivinggeo-location information from the SPS satellites (e.g., GPS). However,it may be assumed that the signal quality from the SPS satellites is notsufficient for accurate position determination. This may occur in indoorenvironments where signals from SPS satellites may be attenuated and/orexperience multipath interference. Such conditions may also beexperienced outdoors in dense urban areas. Accordingly, accurateposition determination may utilize, or at least include in addition toinformation produced by an SPS, signals provided by one or more wirelesscommunication networks.

The operating environment 300 may also include a plurality of one ormore types of Wide Area Network Wireless Access Points (WAN-WAPs) 304a-304 c, which may be used for wireless voice and/or data communication,and as another source of independent position information for mobilestation 301. The WAN-WAPs 304 a-304 c may be part of a wireless widearea network (WWAN), which may include cellular base stations at knownlocations, and/or other wireless wide area systems, such as, forexample, WiMAX (e.g., 802.16). The WWAN may include other known networkcomponents which are not shown in FIG. 3 for simplicity. Typically, eachWAN-WAP 304 a-304 c within the WWAN may operate from fixed positions,and may provide network coverage over large metropolitan and/or regionalareas.

The operating environment 300 may further include Local Area NetworkWireless Access Points (LAN-WAPs) 306 a-306 d, may be used for wirelessvoice and/or data communication, as well as another independent sourceof position data. The LAN-WAPs 306 a-306 d can be part of a WirelessLocal Area Network (WLAN), which may operate in buildings and performcommunications over smaller geographic regions than a WWAN. SuchLAN-WAPs 306 a-306 d may be part of, for example, WiFi networks(802.11x), cellular piconets and/or femtocells, Bluetooth Networks, UWBbeacon, Near Field Communication (NFC) devices, etc.

The mobile station 301 may derive position information and enhanceposition determination using Pairwise Comparison and Compensation (PCC)with any one or a combination of the WAN-WAPs 304 a-304 c, and/or theLAN-WAPs 306 a-306 d. Each of the aforementioned systems can provide anindependent estimate of the position for mobile station 301 usingdifferent techniques as noted above. In some embodiments, the mobilestation 301 may combine the solutions derived from each of the differenttypes of access points to improve the accuracy of the position data andthe PCC process.

When deriving position from the WWAN, each WAN-WAP 304 a-304 c may takethe form of base stations within a digital cellular network, and themobile station 301 may include a cellular transceiver and processor thatcan exploit the base station signals to derive position. It should beunderstood that digital cellular network may include additional basestations or other resources not shown in FIG. 3. While WAN-WAPs 304a-304 c may actually be moveable or otherwise capable of beingrelocated, for illustration purposes it will be assumed that they areessentially arranged in a fixed position. When using cellular networks,the mobile station 301 may perform position determination using theaforementioned time-of-arrival techniques such as, for example, RTTbased measurements, Advanced Forward Link Trilateration (AFLT), etc.Position determination may also be performed based on signal amplitudemeasurements (e.g., RSSI measurements). Moreover, positioningdetermination may be enhanced using the PCC techniques described herein.

In other embodiments, each WAN-WAP 304 a-304 c may take the form ofWiMax wireless networking base station. In this case, the mobile station301 may determine its position using time-of-arrival (TOA) techniques,including RTT based measurements, from signals provided by the WAN-WAPs304 a-304 c, and/or exploiting amplitude information of signals (e.g.,RSSI-based measurements).

The mobile station 301 may determine positions either in a standalonemode, or by using the assistance of a positioning server 310 and network312, as will be described in more detail below. Moreover, positioningserver 310 may be able to receive pairwise measurements from the mobilestation 301, and perform PCC to determine compensation values (e.g.,bias). The compensation values may be transmitted back to the mobilestation 301 for use in compensating measurements (e.g., RSSI and/or RTT)to improve range estimates. Note that embodiments of the disclosureinclude having the mobile station 301 determine position informationusing WAN-WAPs 304 a-304 c which are different types. For example, someWAN-WAPs 304 a-304 c may be cellular base stations, and other WAN-WAPsmay be WiMax base stations. In such an operating environment, the mobilestation 301 may be able to exploit the signals from each different typeof WAN-WAP, and further combine the derived position solutions toimprove accuracy.

When deriving position and/or performing the PCC process using the WLAN,the mobile station 301 may utilize position determination and/or PCCtechniques with the assistance of the positioning server 310 and thenetwork 312. The positioning server 310 may communicate to the mobilestation 301 through network 312. Network 312 may include a combinationof wired and wireless networks which incorporate the LAN-WAPs 306 a-306d. In one embodiment, each LAN-WAP 306 a-306 d may be, for example, aWiFi wireless access point, which is not necessarily set in a fixedposition and can change location. The position of each LAN-WAP 306 a-306d may be stored in the positioning server 310 in a common coordinatesystem, or within the LAN-WAP itself. In one embodiment, the position ofthe mobile station 301 may be determined by having the mobile station301 receive signals from each LAN-WAP 306 a-306 d. Each signal may beassociated with its originating LAN-WAP based upon some form ofidentifying information that may be included in the received signal(such as, for example, a MAC address). The mobile station 301 may thenderive the time delays (e.g., RTT) and/or amplitude information (e.g.RSSI) associated with each of the received signals. The mobile station301 may then form a message which can include the time delays and theidentifying information of each of the LAN-WAPs 306 a-306 d, and sendthe message via network 312 to the positioning server 310. Based uponthe received message, the positioning server 310 may then determine aposition, using the stored locations of the relevant LAN-WAPs 306 a-306d, of the mobile station 301. The positioning server 310 may generateand provide a Location Configuration Information (LCI) message to thebase station that includes a pointer to the mobile station's position ina local coordinate system. The LCI message may also include other pointsof interest in relation to the location of the mobile station 301. Whencomputing the position of the mobile station 301, the positioning server310 may take into account the different delays which can be introducedby elements within the wireless network. The positioning server 310 mayfurther receive pairwise measurements (e.g., RSSI and/or RTT) from eachLAN-WAP 306 a-306 d and the mobile station 301, and perform pairwisecomparison on the measurements to detect and discard outliers. For theremaining measurements, the positioning server 310 may determinecompensation values (e.g., RTT and/or RSSI bias values) for makingadjustments to the measurements, and provide these values to the mobilestation 301 to improve the mobile station's ranging determination andrange-based positioning. In other embodiments, the positioning server310 may provide the received pairwise measurements from another node inthe network, such as any LAN-WAP 306 a-306 d (or WAN-WAP 304 a-304 c)and perform PCC to provide compensation values (e.g., RTT and/or RSSIbias values) for improving range determination and range-basedpositioning.

The position determination techniques described herein may be used forvarious wireless communication networks such as a wide area wirelessnetwork (WWAN), a wireless local area network (WLAN), a wirelesspersonal area network (WPAN), and so on. The term “network” and “system”may be used interchangeably. A WWAN may be a Code Division MultipleAccess (CDMA) network, a Time Division Multiple Access (TDMA) network, aFrequency Division Multiple Access (FDMA) network, an OrthogonalFrequency Division Multiple Access (OFDMA) network, a Single-CarrierFrequency Division Multiple Access (SC-FDMA) network, a WiMax (IEEE802.16) and so on. A CDMA network may implement one or more radio accesstechnologies (RATs) such as cdma2000, Wideband-CDMA (W-CDMA), and so on.Cdma2000 includes IS-95, IS-2000, and IS-856 standards. A TDMA networkmay implement Global System for Mobile Communications (GSM), DigitalAdvanced Mobile Phone System (D-AMPS), or some other RAT. GSM and W-CDMAare described in documents from a consortium named “3rd GenerationPartnership Project” (3GPP). Cdma2000 is described in documents from aconsortium named “3rd Generation Partnership Project 2” (3GPP2). 3GPPand 3GPP2 documents are publicly available. A WLAN may be an IEEE802.11x network, and a WPAN may be a Bluetooth network, an IEEE 802.15x,or some other type of network. The techniques may also be used for anycombination of WWAN, WLAN and/or WPAN.

FIG. 4 is a block diagram illustrating various components of anexemplary mobile station 400. For the sake of simplicity, the variousfeatures and functions illustrated in the box diagram of FIG. 4 areconnected together using a common bus which is meant to represent thatthese various features and functions are operatively coupled together.Those skilled in the art will recognize that other connections,mechanisms, features, functions, or the like, may be provided andadapted as necessary to operatively couple and configure an actualportable wireless device. Further, it is also recognized that one ormore of the features or functions illustrated in the example of FIG. 4may be further subdivided, or two or more of the features or functionsillustrated in FIG. 4 may be combined.

The mobile station 400 may include one or more wide area networkwireless transceiver(s) 404 that may be connected to one or moreantennas 402. The wide area network wireless transceiver 404 comprisessuitable devices, hardware, and/or software for communicating withand/or detecting signals to/from WAN-WAPs 304 a-304 c, and/or directlywith other wireless devices within a network. In one aspect, the widearea network wireless transceiver 404 may comprise a CDMA and/or LTEcommunication system suitable for communicating with a CDMA and/or LTEnetwork of wireless base stations; however in other aspects, thewireless communication system may comprise another type of cellulartelephony network, such as, for example, TDMA or GSM. Additionally, anyother type of wireless networking technologies may be used, for example,WiMax (802.16), etc. The mobile station 400 may also include one or morelocal area network wireless transceivers 406 that may be connected toone or more antennas 402. The local area network wireless transceiver406 comprises suitable devices, hardware, and/or software forcommunicating with and/or detecting signals to/from LAN-WAPs 306 a-306d, and/or directly with other wireless devices within a network. In oneaspect, the local area network wireless transceiver 406 may comprise aWiFi (802.11x) communication system suitable for communicating with oneor more wireless access points; however in other aspects, the local areanetwork wireless transceiver 406 may comprise any another type of localarea network and/or personal area network, (e.g., Bluetooth).Additionally, other types of wireless networking technologies may beused, such as, for example, Ultra Wide Band, ZigBee, wireless USB etc.

As used herein, the abbreviated term “access point” (AP) may be used torefer to LAN-WAPs 306 a-306 d and/or WAN-WAPs 304 a-304 c. Specifically,in the description presented below, when the term “AP” is used, itshould be understood that embodiments may include a mobile station 400that can exploit signals from a plurality of LAN-WAPs 306 a-306 d, aplurality of WAN-WAPs 304 a-304 c, or any combination of the two. Thespecific type of AP being utilized by the mobile station 400 may dependupon the environment of operation. Moreover, the mobile station 400 maydynamically select between the various types of APs in order to arriveat an accurate position solution and/or Pairwise Comparison andCompensation.

An SPS receiver 408 may also be included in mobile station 400. The SPSreceiver 408 may be connected to the one or more antennas 402 forreceiving satellite signals. The SPS receiver 408 may comprise anysuitable hardware and/or software for receiving and processing SPSsignals. The SPS receiver 408 may request information from the othersystems, and perform the calculations necessary to determine the mobilestation's 400 position using measurements obtained by any suitablealgorithm which exploits SPS signals.

A motion sensor 412 may be coupled to a processor 410 to providerelative movement and/or orientation information which is independent ofmotion data derived from signals received by the wide area networkwireless transceiver 404, the local area network wireless transceiver406, and the SPS receiver 408. By way of example, but not limitation,motion sensor 412 may utilize an accelerometer (e.g., a MEMS device), agyroscope, a geomagnetic sensor (e.g., a compass), an altimeter (e.g., abarometric pressure altimeter), and/or any other type of movementdetection sensor. Moreover, motion sensor 412 may include a plurality ofdifferent types of devices and combine their outputs in order to providemotion information.

A processor 410 may be connected to the wide area network wirelesstransceiver 404, local area network wireless transceiver 406, the SPSreceiver 408, and the motion sensor 412. The processor may include oneor more microprocessors, microcontrollers, and/or digital signalprocessors that provide processing functions, as well as othercommunication and control functionality. The processor 410 may alsoinclude memory 414 for storing data and software instructions forexecuting programmed functionality within the mobile station 400. Thememory 414 may be on-board the processor 410 (e.g., within the same ICpackage), and/or the memory 414 may be external memory to the processorand functionally coupled over a data bus. The details of softwarefunctionality associated with aspects of the disclosure will bediscussed in more detail below.

A number of software modules and data tables may reside in memory 414and be utilized by the processor 410 in order to manage bothcommunications, positioning determination, and PCC functionality. Asillustrated in FIG. 4, memory 414 may include and/or otherwise receive apositioning module 416, an application module 418, a received signalstrength indicator (RSSI) module 420, and a round trip time (RTT) module422, and a Pairwise Comparison and Compensation (PCC) module 426. Oneshould appreciate that the organization of the memory contents as shownin FIG. 4 is merely exemplary, and as such, the functionality of themodules and/or data structures may be combined, separated, and/or bestructured in different ways depending upon the implementation of themobile station 400.

The application module 418 may be a process running on the processor 410of the mobile station 400, which requests position information from thepositioning module 416. Applications typically run within an upper layerof the software architectures, and may include, for example, IndoorNavigation, Buddy Locator, Shopping and Coupons, Asset Tracking, andlocation Aware Service Discovery. The positioning module 416 may derivethe position of the mobile station 400 using ranging information derivedfrom the RTT and RSSI values, measured from signals exchanged with aplurality of APs. The ranges derived from RTT and RSSI values may bedetermined in RTT module 422 and RSSI module 420, respectively. In orderto accurately determine position using range-based techniques, pairwisemeasurements between the mobile station 400 and each AP may begenerated, and passed to the PCC module 426. Statistics may be generatedfrom the pairwise measurements (such parameters as averages, variances,medians, etc. may be computed) and comparisons made to detect and removeoutlier measurements. PCC module 426 may then derive compensation valuesassociated with each wireless channel associated with the mobile station400/AP pairs. These compensation values, such as RTT and RSSI biases,may then be provided to RTT module 422 and/or RSSI module 420 to improvethe estimates of range based on measuring the RSSI and RTT of signalsover the wireless channels. These compensation values may also be storedin the parameter database 424 for future use. PCC module 426 may alsoprovide pairwise measurements to other devices upon request, when thepaired device on the opposite side of the wireless channel is performingPCC operations to compensate its own range-based positioning. In someoperational modes, other devices, as noted above, may include otherneighboring mobile stations. Once the improved compensated rangeestimates are performed in the RTT module 422 and the RSSI module 420,the compensated range values may be passed to the positioning module 416to determine an improved position of the mobile station 400.

While the modules shown in FIG. 4 are illustrated in the example asbeing contained in memory 414, it is recognized that in certainimplementations such procedures may be provided for or otherwiseoperatively arranged using other or additional mechanisms. For example,all or part of positioning module 416, PCC module 426, and/orapplication module 418 may be provided in firmware. Additionally, whilein this example positioning module 416 and application module 418 areillustrated as being separate features, it is recognized, for example,that such procedures may be combined together as one procedure orperhaps with other procedures, or otherwise further divided into aplurality of sub-procedures.

Processor 410 may include any form of logic suitable for performing atleast the techniques provided herein. For example, processor 410 may beoperatively configurable based on instructions in memory 414 toselectively initiate one or more routines that exploit motion data foruse in other portions of the mobile device.

The mobile station 400 may include a user interface 450 which providesany suitable interface systems, such as a microphone/speaker 452, keypad454, and display 456 that allows user interaction with the mobilestation 400. The microphone/speaker 452 provides for voice communicationservices using the wide area network wireless transceiver 404 and/or thelocal area network wireless transceiver 406. The keypad 454 comprisesany suitable buttons for user input. The display 456 comprises anysuitable display, such as, for example, a backlit LCD display, and mayfurther include a touch screen display for additional user input modes.

As used herein, mobile station 400 may be any portable or movable deviceor machine that is configurable to acquire wireless signals transmittedfrom, and transmit wireless signals to, one or more wirelesscommunication devices or networks. As shown in FIGS. 3 and 4, the mobilestation is representative of such a portable wireless device. Thus, byway of example but not limitation, mobile station 400 may include aradio device, a cellular telephone device, a computing device, apersonal communication system (PCS) device, or other like movablewireless communication equipped device, appliance, or machine. The term“mobile station” is also intended to include devices which communicatewith a personal navigation device (PND), such as by short-rangewireless, infrared, wire line connection, or other connection—regardlessof whether satellite signal reception, assistance data reception, and/orposition-related processing occurs at the device or at the PND. Also,“mobile station” is intended to include all devices, including wirelesscommunication devices, computers, laptops, etc. which are capable ofcommunication with any server, such as via the Internet, WiFi, or othernetwork, and regardless of whether satellite signal reception,assistance data reception, and/or position-related processing occurs atthe device, at a positioning server, or at another device associatedwith the network. Any operable combination of the above are alsoconsidered a “mobile station.” As used herein, the term “wirelessdevice” may refer to any type of wireless communication device which maytransfer information over a network and also have position determinationand/or navigation functionality. The wireless device may be any cellularmobile terminal, personal communication system (PCS) device, personalnavigation device, laptop, personal digital assistant, or any othersuitable mobile device capable of receiving and processing networkand/or SPS signals.

FIG. 5 is a block diagram illustrating various components of anexemplary local area network access point (LAN-WAP) 500. The LAN-WAP 500may include one or more local area network transceiver(s) 506 that maybe connected to one or more antennas 502. The local area networktransceiver 506 comprises suitable devices, hardware, and/or softwarefor communicating with and/or detecting signals to/from LAN-WAPs 306a-306 d, and/or directly with other wireless devices within a network.In one aspect, the local area network transceiver 506 may comprise aWiFi (802.11x) communication system suitable for communicating with themobile station 400 and/or one or more other local wireless accesspoints; however in other aspects, the local area network transceiver 506may comprise another type of local area network, or personal areanetwork, (e.g., Bluetooth). Additionally, any other type of wirelessnetworking technologies may be used, for example, Ultra Wide Band,ZigBee, wireless USB etc. The LAN-WAP 500 may further include a wirednetwork interface 526 for communicating with local area network 528,which may further be interconnected with a wide area network via a wiredinterface.

A processor 510 may be connected to the local area network transceiver506, and the wired network interface 526. The processor 510 may includeone or more microprocessors, microcontrollers, and/or digital signalprocessors that provide processing functions, as well as othercalculation and control functionality. The processor 510 may alsoinclude memory 514 for storing data and software instructions forexecuting programmed functionality within the LAN-WAP 500. The memory514 may be on-board the processor 510 (e.g., within the same ICpackage), and/or the memory 514 may be external memory to the processorand functionally coupled over a data bus. The details of softwarefunctionality associated with aspects of the disclosure will bediscussed in more detail below.

A number of software modules and data tables may reside in memory 514and be utilized by the processor 510 in order to manage bothcommunications, positioning determination and PCC functionality withinLAN-WAP 500. As illustrated in FIG. 5, memory 514 may include and/orotherwise receive a positioning module 516, a received signal strengthindicator (RSSI) module 520, and a round trip time (RTT) module 522, anda Pairwise Comparison and Compensation (PCC) module 518. One shouldappreciate that the organization of the memory contents as shown in FIG.5 is merely exemplary, and as such the functionality of the modulesand/or data structures may be combined, separated, and/or be structuredin different ways depending upon the implementation of the LAN-WAP 500.

The positioning module 516 may derive the position of the LAN-WAP 500and/or the mobile station 301 using ranging information derived from theRTT and RSSI values, as measured from signals exchanged with a pluralityof neighboring APs and/or the mobile station 301. The ranges derivedfrom RTT and RSSI values may be determined in RTT module 522 and RSSImodule 520, respectively. In order to accurately determine positionusing range-based techniques, pairwise measurements between the mobilestation 301 and each neighboring LAN-WAPs 306 a-306 d may be generated,and passed to the PCC module 518. Statistics (mean/average, weightedaverage, variance, median, etc.) may be generated from the pairwisemeasurements, and comparisons made to detect and remove outliermeasurements. PCC module 518 may then derive compensation (adjustment)values associated with each wireless channel associated with the mobilestation 301 and LAN-WAPs 306 a-306 d pairs. These compensation values,such as RTT and RSSI biases, may then be provided to RTT module 522and/or RSSI module 520 to improve the estimates of range based onmeasuring the RSSI and RTT of signals over the wireless channels. Thesecompensation values may also be stored in the parameter database 524 forfuture use. PCC module 518 may also provide pairwise measurements toother devices upon request, when the paired device on the opposite sideof the wireless channel is performing PCC operations to compensate itsown range-based positioning.

Once the improved compensated range estimates are performed in the RTTmodule 522 and the RSSI module 520, the compensated range values may bepassed to the positioning module 516 to determine an improved positionof the mobile station 301.

While the modules shown in FIG. 5 are illustrated in the example asbeing contained in memory 514, it is recognized that in certainimplementations such procedures may be provided for or otherwiseoperatively arranged using other or additional mechanisms. For example,all or part of positioning module 516, RSSI module 520, RTT module 522,and/or PCC module 518 may be provided in firmware. Additionally, whilein this example positioning module 516 and the PCC module 518 areillustrated as being separate features, it is recognized, for example,that such procedures may be combined together as one procedure orperhaps with other procedures, or otherwise further divided into aplurality of sub-procedures.

Processor 510 may include any form of logic suitable for performing atleast the techniques provided herein. For example, processor 510 may beoperatively configurable based on instructions in memory 514 toselectively initiate one or more routines that exploit motion data foruse in other portions of the LAN-WAP 500. As used herein, the LAN-WAP500 may be any portable or movable device or machine that isconfigurable to acquire wireless signals transmitted from, and transmitwireless signals to, one or more wireless communication devices ornetworks.

FIG. 6 is a block diagram illustrating various components of anexemplary positioning server 600. The positioning server 600 may includea processor 605, a system bus 607, a mass storage unit 620, an I/Ointerface 615, a memory unit 610, and a network interface 625. Theprocessor 605 may interface with memory 610 and the mass storage unit620 via the system bus 607. The memory 610 and/or the mass storage unit620 may contain executable instructions in the form of software modulesand data in a parameter database for implementing various operations forperforming the PCC operations described herein. The network interface625 may interface with the processor 605 over the system bus 607, andcan provide an interface for communication with the network 602. The I/Ointerface 615 may be provided to permit a user to interface to thepositioning server 600 via user interface 630. The positioning server600 may be any type of computer/server utilizing any suitable operatingsystem. Alternatively, the positioning server 600 may be implemented asspecial purpose hardware.

The software modules and data tables may reside in memory 610 and/ormass storage 620 can be utilized by the processor 605 in order to manageperform PCC operations and/or positioning determination the wirelessnetwork. As illustrated in FIG. 6, memory 610 may include and/orotherwise receive a positioning module 642, a received signal strengthindicator (RSSI) module 646, and a round trip time (RTT) module 644, anda Pairwise Comparison and Compensation (PCC) module 640. One shouldappreciate that the organization of the memory contents as shown in FIG.6 is merely exemplary, and as such the functionality of the modulesand/or data structures may be combined, separated, and/or be structuredin different ways depending upon the implementation of the positioningserver 600.

The positioning server 600 may receive RSSI and/or RTT measurements froma node of interest for which PCC operations are desired (hereinafter“node”). The node may be a mobile station 301, and/or an AP, such as,for example, a WAN-WAPs 304 a-304 c and/or LAN-WAPs 306 a-306 d. TheRSSI and/or RTT measurements may be received from the node over network602. These values may be used to perform PCC operations for the node,and subsequently provide compensation/adjustment values (e.g., RTTand/or RSSI bias values) back to the node over network 602. Thepositioning server 600 may also determine the position of the node usingpositioning module 642 using ranging information derived from the RTTand RSSI values received from the node. The ranges may be derived fromRTT and RSSI values determined in RTT module 644 and RSSI module 646,respectively.

In order to accurately determine position using range-based techniques,pairwise measurements between the node and the neighboring nodes may bereceived by the positioning server 600, and passed to the PCC module640. Statistics may be generated from the pairwise measurements, andcomparisons made to detect and remove outlier measurements. PCC module640 may then derive compensation values associated with each wirelesschannel associated with the node pairs. These compensation values maythen be provided to RTT module 644 and/or RSSI module 646 to improve theestimates of range based on measuring the RSSI and RTT of signals overthe wireless channels. These compensation values may also be stored inthe parameter database 635 for future use. Once the improved compensatedrange estimates are performed in the RTT module 644 and the RSSI module646, the compensated range values may be passed to the positioningmodule 642 to determine an improved position of the node, which then maybe passed back to the node over the network 602.

In summary, the positioning server 600 may perform positiondetermination enhancement by receiving measurements from a first nodebased on signals received from a plurality of neighboring nodes. Theserver may further receive signal measurements from a plurality ofneighboring nodes based on signals received from the first node. Theserver may then determine a pairwise comparison of the measurements fromthe first node and the measurements from each neighboring node, and thencompensate the measurements received from the node based on the pairwisecomparisons. The server may then provide the compensation parameter(s),such as the bias, to the first node so it may determine position.Alternatively, the positioning server 600 itself may determine aposition estimate of the first node using the compensated measurements.

While the modules shown in FIG. 6 are illustrated in the example asbeing contained in memory 610, it is recognized that in certainimplementations such procedures may be provided for or otherwiseoperatively arranged using other or additional mechanisms. For example,all or part of positioning module 642, RSSI module 646, RTT module 644,and/or PCC module 640 may be provided in firmware. Additionally, whilein the example positioning module 642 and the PCC module 640 areillustrated as being separate modules, it is recognized, for example,that such procedures may be combined together as one procedure orperhaps with other procedures, or otherwise further divided into aplurality of sub-procedures.

FIG. 7 is a flowchart showing an exemplary process 700 for pairwisecomparison and compensation (PCC) of ranging measurements and subsequentposition determination of a node of interest. The process may start byperforming a collection of pairwise measurements, which may include RTTand/or RSSI values, between pairs of nodes in the wireless network(705). The collection of pairwise measurements may be made between anode of interest (for which an enhanced position measurement may bedesired) and a plurality of neighboring nodes. A single pairwisemeasurement occurs between the node of interest and a neighboring nodeacross a shared wireless channel. The single pairwise measurementproduces two measurements representative of the same signalcharacteristic (e.g., RSSI, RTT, etc.) observed from opposite ends ofthe shared wireless channel. The shared wireless channel may ideally bethe same, and is hereinafter referred to as the “same wireless channel.”

In other words, the pairwise measurement may be thought of as the resultof measuring a quantity between two nodes over the same wireless channelin opposite directions. For example, the pairwise measurement may beperformed by having a node of interest perform one or more measurementsusing signals received by a neighboring node. The same quantities may bemeasured in the opposite direction at the neighboring node using signalsprovided by the node of interest. Once the measurements are completed bythe neighboring node, the results may be transmitted back to the node ofinterest. The pairwise measurements between the aforementioned node pairmay be repeated to produce statistically reliable results. Additionalpairwise measurements between the node of interest and other neighboringnodes may be performed to generate the collection of pairwisemeasurements. The process 700 may be performed between any types ofnodes in the wireless network (e.g., the mobile station 301, theLAN-WAPs 306 a-306 d and/or the WAN-WAPs 304 a-304 c). These pairwisemeasurements may be shared between nodes for processing, and/or sent tothe positioning server 600 for PCC and/or position determination.

Next, a pairwise comparison step may be performed on the pairwisemeasurements to detect and remove outliers (710). This may includedetermining differences between each measurement pair, and computingstatistics of the measurement pair (such as a mean, average, median,variance, standard deviation, etc.), which may be combined to calculatean overall uncertainty parameter per wireless channel. The uncertaintyparameter may be used determine a test as to whether outliers arepresent in the pairwise measurements, which may utilize a predeterminedthreshold and/or a calculated threshold which is adjusted as moremeasurements are determined. Either type of threshold is referred toherein as a measurement error threshold, and may be an RTT thresholdand/or an RSSI threshold. When an outlier is detected, (i.e., themeasurement fails a quality test), the outlier measurement may bediscarded (730). Discarding the outliers may improve the quality of thepairwise measurements, and thus increase the accuracy of the subsequentrange and position determination operations.

Pairwise measurements which have passed the quality test and are notdiscarded will be used to determine pairwise compensation values (715).Here, paired measurements which passed the comparison block (710) may beused to compute compensation estimates, such as RTT bias estimatesand/or RSSI bias estimates. Once these compensation values aredetermined, they may be applied to the pairwise measurements. In anembodiment, the pairwise RSSI measurements may be adjusted to have thecomputed RSSI bias removed, and the pairwise RTT measurements may beadjusted to have the RTT bias removed for each wireless channelassociated with the node of interest. These compensated pairwisemeasurements may be further processed statistically, and/or weightedbased on the channel uncertainty computed in block (710). Theprocessed/weighted measurements determined in block (715) may then beused to determine corresponding ranges, and then an enhanced positionestimate of the node using range-based position determination (720). Theenhanced position estimate may be delivered to a requesting entity(725), such as an application (e.g., a navigation app) running on themobile station 301.

FIG. 8 is a flowchart showing an exemplary process 800 for pairwisecalibration when a neighboring node is pre-calibrated. This processpermits the calibration accuracy of the pre-calibrated device to be“propagated” to other nodes within the network. Moreover, process 800may be performed within any node in the wireless network (e.g., themobile station 301, the LAN-WAPs 306 a-306 d and/or the WAN-WAPs 304a-304 c). Initially, the method may start out similarly as block 705 inFIG. 7 as described above, where pairwise measurement collection isperformed (e.g., RTT and/or RSSI measurements) from availableneighboring devices (805). These pairwise measurements may be sharedbetween nodes, or sent to the positioning server 600. Each pair ofdevices may generate multiple pairwise measurements over a commonwireless channel.

Next, the node may determine if any neighboring node is a calibratedtarget device (810). This may be performed by having the neighboringnode provide a reliability indicator directly to the node, or indirectlythrough a parameter via the positioning server 310. If there are notarget calibrated devices available, the process will perform the PCCprocess 700 shown in FIG. 7 (820). However, if a target calibrationdevice exists, pairwise calibration may be performed based on thecalibrated device (815). This may be performed by calculating statisticsof the pairwise RSSI measurements (e.g., perform an average or mean ofthe RSSI values). Pairwise differences of RSSI and RTT may then bedetermined. The bias estimate for the RSSI values may be determined bycalculating the mean of the pairwise RSSI differences. The bias estimatefor the RTT values may be determined by calculating the mean of thepairwise RTT differences. The estimated bias values may be stored in theparameter database of the node, or in the parameter database of thepositioning sever 310, for use in future pairwise calibration with othernodes. In alternative embodiments, a confidence level of the calibrationinformation associated with a calibrated device may be determined. Thisconfidence level may be based on evaluating the statistics of thepairwise measurements described above in relation to the calibrationinformation of the calibrated device for one or more nodes. A weightingvalue for the bias values may be determined/adjusted based upon theconfidence level.

FIG. 9 is a flowchart showing an exemplary process 900 for triggeringpairwise comparison and compensation. This process may monitor RSSI andRTT values over time, and perform PCC to reduce their variance if theydrift too much as time progresses. The use of triggering alleviates anode from having to perform ongoing PCC as the node operates in thenetwork.

Initially, the process 900 may start out similarly as block 705 in FIG.7 as described above, where pairwise measurement collection is performed(e.g., RTT and/or RSSI measurements) from available neighboring devices(905). These pairwise measurements may be shared between nodes, or sentto the positioning server 600. Each pair of devices may generatemultiple pairwise measurements over a common wireless channel.

A sample variation check may then be performed (910). This samplevariation may be determined by computing the statistics of the RSSImeasurements determined at the node of interest. A failure may bedeclared if the mean RSSI is lower than an RSSI threshold. When afailure is declared, the PCC process 700 is triggered for the wirelesschannel associated with failed RSSI measurement (935). Variousstatistical measurements, such as variance calculation, ANOVA, etc., maybe performed to assess the variation of the measurements in block 910.

If the RSSI measurement passes the sample variation check in block 910,a consistency check between the RSSI and the RTT values may be performed(915). Here, the ranges between the node and a neighboring node may bedetermined based on the RTT values. This range may be converted to anexpected RSSI value using known models. If the difference between theexpected RSSI and the measured RSSI is higher than a threshold (e.g.,referred to herein as an “RSSI-range threshold”), then a failure may bedeclared. Similar checks may be made on the RTT values using anRTT-range threshold. When a failure is declared, the PCC process 700 istriggered for the failed wireless channel (935). In summary, theconsistency check between RTT and RSSI values may include determining arange corresponding to an RTT measurement associated with a givenneighboring node; determining an expected RSSI value based on thedetermined range; comparing, based on an RSSI threshold, the expectedRSSI value with the RSSI measurement associated with the givenneighboring node; and indicating that the RSSI measurement isinconsistent with the RTT measurement when the comparison exceeds theRSSI threshold.

Summarizing blocks 910 and 915, process 900 may evaluate the quality ofthe RTT and RSSI measurements received from the neighboring nodes. Whenthe pairwise RTT and/or RSSI measurements fail the evaluation, PCC maybe triggered with each neighboring node associated with the measurementswhich fail the evaluation.

If the RSSI and RTT values for the node of interest pass the evaluationtests in block 910 and block 915, range based positioning of the nodemay be performed using the checked RSSI and RTT values to determine theranges (920). A post positioning measurement check may then be performed(925). Here, the ranges to each neighboring node may be computedgeometrically using the position determined in block 920 and the knownpositions of the neighboring nodes. If the difference between thegeometric range and the range determined using the RTT exceeds athreshold (e.g., an RTT-range threshold) for given wireless channel, therange value fails, and the PCC process 700 is triggered for the failedwireless channel (935). Thus, process 900 may compare information basedon the measurements with information derived from the determinedposition estimate, and performing pairwise comparison and compensationwith each neighboring node associated with RTT measurements and/or RSSImeasurements (where the RSSI ranges may be compared against anRSSI-range threshold) which compare unfavorably (i.e., fails to pass thethreshold test). However, if the measurements for the node pass thepost-positioning measurement check in block 925, and thus favorablycompare, the position of the node of interest is validated, and may thenbe delivered to the requested application (930).

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The methods, sequences and/or algorithms described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

While the foregoing disclosure shows illustrative embodiments of theinvention, it should be noted that various changes and modificationscould be made herein without departing from the scope of the inventionas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the embodiments of the inventiondescribed herein need not be performed in any particular order.Furthermore, although elements of the invention may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

What is claimed is:
 1. A method for triggering an enhanced a positionestimate of a first node using pairwise measurements, comprising:receiving Round Trip Time (RTT) and Received Signal Strength Indicator(RSSI) measurements from a plurality of neighboring nodes, wherein theRTT and RSSI measurements are performed at the neighboring nodes using asignal provided by the first node; evaluating a quality of the RTT andRSSI measurements received from the neighboring nodes, and performingpairwise comparison and compensation with each neighboring nodeassociated with the RTT and/or RSSI measurements which fail theevaluating; determining a position estimate of the first node based onthe RTT measurements and RSSI measurements which pass the evaluating;and comparing information based on the RTT measurements and/or the RSSImeasurements with information derived from the position estimate, andperforming pairwise comparison and compensation with each neighboringnode associated with RTT measurements and/or RSSI measurements whichcompare unfavorably.